3,788 research outputs found
Mass Deformed Exact S-parameter in Conformal Theories
We use the exact expression for the S parameter in the perturbative region of
the conformal window to establish its dependence on the explicit introduction
of fermion masses. We demonstrate that the relative ordering with which one
sends to zero either the fermion mass or the external momentum leads to
drastically different limiting values of S. Our results apply to any fermion
matter representation and can be used as benchmark for the determination of
certain relevant properties of the conformal window of any generic vector like
gauge theory with fermionic matter. We finally suggest the existence of a
universal lower bound on the opportunely normalized S parameter and explore its
theoretical and phenomenological implications. Our exact results constitute an
ideal framework to correctly interpret the lattice studies of the conformal
window of strongly interacting theories.Comment: 4 pages, 2 figures. 2column
Nonperturbative Results for Yang-Mills Theories
Some non perturbative aspects of the pure SU(3) Yang-Mills theory are
investigated assuming a specific form of the beta function, based on a recent
modification by Ryttov and Sannino of the known one for supersymmetric gauge
theories. The characteristic feature is a pole at a particular value of the
coupling constant, g. First it is noted, using dimensional analysis, that
physical quantities behave smoothly as one travels from one side of the pole to
the other. Then it is argued that the form of the integrated beta function
g(m), where m is the mass scale, determines the mass gap of the theory.
Assuming the usual QCD value one finds it to be 1.67 GeV, which is in
surprisingly good agreement with a quenched lattice calculation. A similar
calculation is made for the supersymmetric Yang-Mills theory where the
corresponding beta function is considered to be exact.Comment: RevTeX, 2colmuns, 6 pages and 7 figure
Composite Higgs to two Photons and Gluons
We introduce a simple framework to estimate the composite Higgs boson
coupling to two-photon in Technicolor extensions of the standard model. The
same framework allows us to predict the composite Higgs to two-gluon process.
We compare the decay rates with the standard model ones and show that the
corrections are typically of order one. We suggest, therefore, that the
two-photon decay process can be efficiently used to disentangle a light
composite Higgs from the standard model one. We also show that the Tevatron
results for the gluon-gluon fusion production of the Higgs either exclude the
techniquarks to carry color charges to the 95% confidence level, if the
composite Higgs is light, or that the latter must be heavier than around 200
GeV.Comment: RevTex 7 pages, 6 figure
Corrigan-Ramond Extension of QCD at Nonzero Baryon Density
We investigate the Corrigan-Ramond extension of one massless flavor Quantum
Chromo Dynamics at nonzero quark chemical potential. Since the extension
requires the fermions to transform in the two index antisymmetric
representation of the gauge group, one finds that the number of possible
channels is richer than in the 't Hooft limit. We first discuss the diquark
channels and show that for a number of colors larger than three a new diquark
channel appears. We then study the infinite number of color limit and show that
the Fermi surface is unstable to the formation of the
Deryagin-Grigoriev-Rubakov chiral waves. We discover, differently from the 't
Hooft limit, the possibility of a colored chiral wave breaking the color
symmetry as well as translation invariance.Comment: RevTeX, 14 pages, 2 figure
Light Composite Higgs from Higher Representations versus Electroweak Precision Measurements -- Predictions for LHC
We investigate theories in which the technifermions in higher dimensional
representations of the technicolor gauge group dynamically break the
electroweak symmetry of the standard model. For the two-index symmetric
representation of the gauge group the lowest number of techniflavors needed to
render the underlying gauge theory quasi conformal is two. We confront the
models with the recent electroweak precision measurements and demonstrate that
the two technicolor theory is a valid candidate for a dynamical breaking of the
electroweak symmetry. The electroweak precision measurements provide useful
constraints on the relative mass splitting of the new leptons needed to cure
the Witten anomaly. In the case of a fourth family of leptons with ordinary
lepton hypercharge the new heavy neutrino can be a natural candidate of cold
dark matter. We also propose theories in which the critical number of flavors
needed to enter the conformal window is higher than the one with fermions in
the two-index symmetric representation, but lower than in the walking
technicolor theories with fermions only in the fundamental representation of
the gauge group. Due to the near conformal/chiral phase transition, we show
that the composite Higgs is very light compared to the intrinsic scale of the
technicolor theory. For the two technicolor theory we predict the composite
Higgs mass not to exceed 150 GeV.Comment: RevTex, 53 pages, 7 figures and two table
Composite Inflation from Super Yang-Mills, Orientifold and One-Flavor QCD
Recent investigations have shown that inflation can be driven by
four-dimensional strongly interacting theories non-minimally coupled to
gravity. We explore this paradigm further by considering composite inflation
driven by orientifold field theories. The advantage of using these theories
resides in the fact that at large number of colors they feature certain super
Yang-Mills properties. In particular we can use for inflation the bosonic part
of the Veneziano-Yankielowicz effective theory. Furthermore, we include the 1/N
as well as fermion mass corrections at the effective Lagrangian level allowing
us to explore the effects of these corrections on the inflationary slow-roll
parameters. Additionally the orientifold field theory with fermionic matter
transforming according to the two-index antisymmetric representation for three
colors is QCD. Therefore this model can be interpreted as a new non-minimally
coupled QCD theory of inflation. The scale of composite inflation, for all the
models presented here, is of the order of GeV. Unitarity studies of
the inflaton scattering suggest that the cutoff of the model is at the Planck
scale.Comment: 17 page
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